docs: Self-hosted kubernetes installation page refactor

[ppawlowski]

Description

This pull request refactors documentation related to FlowFuse installation on Kubernetes environment.
New layout is aligned with a one applied on a Docker installation page. Also, it solves problems defined during evaluation of current installation description.

Related Issue(s)

Closes #4634

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production

Labels

• Includes a DB migration? -> add the area:migration label

[hardillb]

Added some comments.

I'm still looking, but it's hard to render the check list locally in VSCode at the moment

[joepavitt]

I'm still looking, but it's hard to render the check list locally in VSCode at the moment

If you run the website locally, you'll see it all rendered live.

[hardillb]

A couple more suggestions, but looks good.